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Area Forecast Discussion

759
FXUS62 KCHS 311045
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
645 AM EDT TUE MAR 31 2015

.SYNOPSIS...
WEAK HIGH PRESSURE ACROSS THE AREA TODAY WILL GIVE WAY TO AN
APPROACHING COLD FRONT TONIGHT. THE FRONT WILL THEN ADVANCE
THROUGH THE REGION WEDNESDAY. HIGH PRESSURE WILL THEN BUILD OVER
THE AREA BEHIND THE FRONT...BEFORE SETTLING OVER THE ATLANTIC
THURSDAY THROUGH FRIDAY. A STRONGER COLD FRONT WILL CROSS THE
REGION LATE FRIDAY NIGHT OR SATURDAY...FOLLOWED BY COOLER HIGH
PRESSURE THROUGH EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
THROUGH MID MORNING...WE/RE CONSIDERABLY WARMER THAN THE PAST
COUPLE OF MORNING IN MANY SECTIONS AND THIS ALONG WITH HIGHER DEW
POINTS HAS ALLOWED FOR PATCHY TO AREAS OF RADIATION FOG TO
DEVELOP. THE WORST CONDITIONS WILL BE OVER SE GA AND MAINLY TO
THE SOUTH OF I-16 WHERE THE LOWEST CONDENSATION PRESSURE DEFICITS
WILL OCCUR. BUT PATCHY FOG WILL STILL OCCUR FURTHER NORTHWARD. A
SPECIAL WEATHER STATEMENT IS IN EFFECT DUE TO VISIBILITIES DOWN TO
1/4 MILE OR LESS.

TODAY...THE REMNANTS OF A DECAYING COOL FRONT WILL FIZZLE OUT OVER
OR NEAR THE FORECAST AREA THIS MORNING...GIVING WAY TEMPORARILY
TO WEAK HIGH PRESSURE. THIS IS BECAUSE A SECOND AND BETTER DEFINED
COLD FRONT WILL DROP SOUTHWARD THROUGH THE OHIO VALLEY AND NE
STATES THIS MORNING...REACHING THE DELMARVA TO KENTUCKY AND
MISSOURI BY DUSK. IN THE MID/UPPER LEVELS WE FIND AN AMPLIFIED
PATTERN WITH A DEEP WEST-NW FLOW. THERE IS A SHORT WAVE EMBEDDED
IN THE FLOW ACROSS THE LOWER MS VALLEY THIS MORNING THAT WILL
TRANSLATE QUICKLY TOWARD SOUTHERN GA BY EVENING. THIS WILL BE
ACCOMPANIED BY MOISTURE TRANSPORT MAINLY IN THE 850-300 MB LAYER
AND ALLOW FOR ISOLATED CONVECTION TO DEVELOP AFTER 4 OR 5 PM AS
THE SHORT WAVE DRAWS CLOSER. THIS LOOKS TO BE CONFINED TO MAINLY
TO LOCATIONS SOUTH OF I-16 AND WEST OF I-95 AFTER THAT TIME. ANY
CAP IS WEAK AND WILL FADE WITH THE APPROACHING SHORT WAVE AND
THERE IS ACTUALLY SOME SURFACE BASED INSTABILITY. SBCAPES ARE AS
HIGH AS 1000-1500 J/KG AND TOTAL TOTALS ARE GREATER THAN 50. THIS
SUGGESTS A FEW T-STORMS. THERE MAY EVEN A FEW STRONG ONES WITH
DOWNBURST WINDS WITH DCAPES OF 500-800 J/KG...PLUS SOME HAIL WITH
WET BULBS AROUND 7-8K FT...CAPE IN THE HAIL GROWTH ZONE OF 300-400
J/KG AND 500 TEMPS AS COLD AS -16 TO -18C. ELSEWHERE TO THE NORTH
AND NE THERE DOESN/T APPEAR TO BE ANY RISK OF CONVECTION TODAY DUE
TO THE LACK OF BOTH FORCING AND SIGNIFICANT MOISTURE.

WE DIDN/T STRAY FAR FROM THE PURE LOW LEVEL THICKNESS FORECAST
GIVEN MANY AREAS OF FULL OR NEAR FULL INSOLATION TO OCCUR BEFORE
CLOUDS START INCREASING AND THICKENING FROM WEST/SW DURING THE
MID AND LATE AFTERNOON. WITH WARM ADVECTION AND DEEP WESTERLIES
OFF THE APPALACHIANS THIS WILL EASILY SUPPORT HIGHS WITHIN A FEW
DEGREES EITHER SIDE OF 80. THE RESULTANT SEA BREEZE WILL HOLD
COASTAL SC INTO THE UPPER 60S...BUT THE GA SHORELINE WILL MAKE IT
INTO THE LOWER AND MIDDLE 70S.

WHILE THERE WON/T BE MUCH WIND THE FIRST HALF OF THE DAY...A
TIGHTENING OF THE GRADIENT IN ADVANCE OF THE UPSTREAM COLD
FRONT...DEEP MIXING AND SOME PRESSURE FALLS LATE WILL ALLOW FOR
WEST/SW WINDS TO CLIMB TO AS HIGH AS 15 OR 20 MPH IN MOST SECTIONS
LATE. WITH ENHANCEMENT FROM THE SEA BREEZE PARTS OF THE CHARLESTON
TRI-COUNTY DISTRICT WILL HAVE GUSTS UP NEAR 25 MPH AT TIMES.

TONIGHT...THE SHORT WAVE PULLS INTO THE ATLANTIC EARLY ON AND IS
FOLLOWED BY ANOTHER SHORT WAVE QUICKLY MOVING THROUGH DURING THE
OVERNIGHT PERIOD. AT THE SAME TIME THE EAST-WEST ALIGNED COLD
FRONT WILL BE DRAWING CLOSER TO THE CWFA BY LATE. ISOLATED TO
SCATTERED SHOWERS WILL PREVAIL THROUGH MIDNIGHT...MAINLY OVER
CENTRAL AND SOUTHERN LOCATIONS WHERE THE DEEPEST MOISTURE WILL BE
FOUND. BUT RAIN CHANCES WILL DWINDLE OVERNIGHT BEHIND THE SECOND
SHORT WAVE. ANY ISOLATED EVENING T-STORMS WILL FADE BY 10 OR 11
PM AS THE NOCTURNAL STABILIZING ENVIRONMENT TAKES OVER.
CONSIDERABLE CLOUDINESS...THE LACK OF ANY INFLUX OF COOLER AIR AND
ELEVATED DEW POINTS WILL PREVENT TEMPS FROM FALLING ANY LOWER THAN
THE MID AND UPPER 50S.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
WEDNESDAY...A SURFACE COLD FRONT WILL PUSH THROUGH THE REGION FROM
THE NORTH...AND HIGH PRESSURE WILL BUILD FROM THE NORTH/NORTHEAST.
31/00 UTC GUIDANCE HAS CONTINUED TO TREND TOWARD A DRIER SOLUTION...
SHUNTING PWATS 1 INCH OR GREATER WELL SOUTH/WEST OF THE FORECAST
AREA. WHILE AN ISOLATED SHOWER/THUNDERSTORM CANNOT BE COMPLETELY
RULED OUT WHERE LOW LEVEL CONVERGENCE IS FOCUSED ACROSS FAR SOUTHERN
COUNTIES...MODEL SOUNDINGS DEPICT A SUBSIDENCE INVERSION/CAPPING OF
SUFFICIENT MAGNITUDE TO HOLD POPS BELOW 15 PERCENT WITH NO MENTION
OF PRECIPITATION. OTHERWISE...HIGH TEMPS SHOULD RANGE FROM THE MID
70S NORTH..A FEW DEGREES COOLER THAN TUESDAY...TO AROUND 80 FAR
INLAND/SOUTH.

WEDNESDAY NIGHT...THE SURFACE HIGH WILL SHIFT INTO THE
ATLANTIC...AND AN UPPER RIDGE AXIS WILL ADVANCE INTO THE REGION. THE
PLUME OF ENHANCED MOISTURE FEATURING PWATS 1.00 TO 1.25 INCH WILL
PIVOT FROM A W-E TO A S-N ORIENTATION AS SOUTHERLY FLOW INTENSIFIES
AND A SHORTWAVE TROUGH FOLLOWS THE UPPER RIDGE INTO LOCATIONS
WEST/SOUTHWEST OF THE FORECAST AREA. BECAUSE OF THE DRY AIR PROVIDED
BY RIDGING AT THE SURFACE AND ALOFT...THIS MOIST PLUME WILL BE HELD
OUTSIDE OF THE FORECAST AREA THROUGH WEDNESDAY NIGHT...AND POPS EVEN
ACROSS FAR SOUTHERN/INLAND COUNTIES HAVE BEEN LOWERED WELL BELOW 10
PERCENT AND THE PREVIOUS MENTION OF SHO0WERS HAS BEEN REMOVED.

THURSDAY...THE UPPER RIDGE WILL PUSH OFFSHORE AND A WEAK BUT
NEGATIVELY UPPER SHORTWAVE TROUGH/ASSOCIATED MOIST PLUME WILL
ADVANCE NORTHEAST INTO THE REGION. THUS...THE CHANCE FOR
SHOWERS/THUNDERSTORMS SHOULD INCREASE...ESPECIALLY THURSDAY
AFTERNOON. DUE TO THE POTENTIAL EFFECTS OF RESIDUAL DRY AIR/CAPPING
INDICATED BY MODEL SOUNDINGS...LIMITED POPS TO SLIGHT
CHANCE/CHANCE...HIGHEST INLAND/FARTHEST FROM OFFSHORE HIGH PRESSURE.

THURSDAY NIGHT...A FEW SHOWERS/THUNDERSTORMS COULD LINGER
NORTH/INLAND DURING THE EVENING. OTHERWISE...EXPECT A MILD NIGHT
WITH LOWS IN THE 60S.

FRIDAY...AHEAD OF AN APPROACHING COLD FRONT THERMAL RIDGING/
COMPRESSIONAL HEATING SHOULD PUSH TEMPERATURES INTO THE LOWER TO MID
80S...AND LOCALLY WARMER TEMPERATURES ARE POSSIBLE INLAND. AN
ISOLATED SHOWER/THUNDERSTORM CANNOT BE RULED OUT IF/WHERE LOW LEVEL
CONVERGENCE DEVELOPS EAST OF I-95...BUT THE POTENTIAL FOR CONVECTION
APPEARS TOO LOW TO JUSTIFY A MENTION WITHIN PUBLIC FORECASTS.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
A COLD FRONT WILL PUSH INTO THE REGION EITHER LATE FRIDAY NIGHT OR
DURING THE DAY SATURDAY. 31/00 UTC GUIDANCE TIMING DIFFERENCES
PERSIST...RANGING FROM A FAST OPERATIONAL GFS WHICH PUSHES THE FRONT
COMPLETELY THROUGH THE REGION EARLY SATURDAY WITH LIMITED CHANCE FOR
CONVECTION TO A SOMEWHAT SLOWER OPERATIONAL EURO WHICH DEPICTS THE
FRONT BISECTING THE FORECAST AREA EARLY SATURDAY AFTERNOON...
SUPPORTING A GREATER CHANCE FOR SHOWERS/THUNDERSTORMS AND PERHAPS
EVEN A POTENTIAL FOR SOME SEVERE WEATHER ESPECIALLY SOUTH/EAST.
MAINTAINED SLIGHT CHANCE/CHANCE POPS FOR SHOWERS/THUNDERSTORMS LATE
FRIDAY NIGHT INTO SATURDAY...BUT FURTHER ADJUSTMENTS COULD BE NEEDED
WITHIN SUBSEQUENT FORECASTS. IN ANY CASE...POST FROPA HIGH PRESSURE
WILL PROVIDE SLIGHTLY COOLER THAN NORMAL TEMPERATURES BY SATURDAY
NIGHT/SUNDAY...FOLLOWED BY A WARMING TREND AS HIGH PRESSURE SHIFTS
OFFSHORE EARLY NEXT WEEK. ALSO...INTRODUCED SLIGHT CHANCE/CHANCE
POPS EARLY NEXT WEEK AS MEDIUM RANGE GUIDANCE DEPICTS INCREASING
MOISTURE SPREADING INTO THE REGION FROM THE WEST. HOWEVER...MODEL
AGREEMENT REGARDING FORECAST DETAILS OF ANY PRECIPITATION REMAINS
POOR EARLY NEXT WEEK.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
VFR WEATHER WILL PREVAIL AT KCHS THROUGH 06Z WEDNESDAY. LOW END
RISK OF SHALLOW GROUND FOG THROUGH 13Z.

AT KSAV...FOG AND LOW STRATUS THIS MORNING WILL LEAD TO LIFR
CONDITIONS CLOSE TO AIRFIELD MINIMUMS THROUGH 13Z...BEFORE
RAPIDLY IMPROVING TO VFR. THERE COULD BE SCATTERED SHRA NEAR THE
TERMINAL TONIGHT...WITH A LOW END RISK OF TSRA.

WEST/SW WINDS WILL BE GUSTY AT BOTH SITES DURING THE MID/LATE
AFTERNOON...PEAKING AROUND 20 KT FROM 19-23Z.

EXTENDED AVIATION OUTLOOK...TRANSIENT FLIGHT RESTRICTIONS POSSIBLE
ESPECIALLY IN SHOWERS/TSTMS THURSDAY AND AGAIN AS A COLD FRONT
CROSSES THE REGION SATURDAY. OTHERWISE...MAINLY VFR.

&&

.MARINE...
TODAY...A DIFFUSE AND SHALLOW COOL FRONT WILL DISSIPATE NEAR OR
OVER THE LOCAL WATERS EARLY...FOLLOWED BY WEAK HIGH PRESSURE. A
LIGHT TO GENTLE WESTERLY FLOW THIS MORNING WILL BACK TO SW WITH
SEA BREEZE CIRCULATIONS AND THE PRESSURE PATTERN WILL BECOME MORE
ENHANCED IN ADVANCE OF A COLD FRONT MOVING INTO THE MID-ATLANTIC
REGION BY LATE. WE/LL NEED TO KEEP A CLOSE WATCH ON CONDITIONS IN
CHARLESTON HARBOR AND ACROSS AMZ350 WHERE WINDS MAY APPROACH
ADVISORY CONDITIONS LATE. FOR NOW WE HAVE CAPPED WINDS AT 15 KT IN
CHARLESTON HARBOR AND 20 KT ON THE CHARLESTON COUNTY 0-20 NM
ATLANTIC WATERS.

TONIGHT...THE GRADIENT TIGHTENS A BIT FURTHER EARLY ON...AND AS
BEFORE WE/LL BE CLOSE TO SMALL CRAFT CRITERIA ON NOT ONLY AMZ350
BUT ALSO AMZ352. BUT THE GRADIENT SLACKENS OVERNIGHT AND WINDS
WILL GRADUALLY DECLINE ON THESE WATERS AND ELSEWHERE.

ISOLATED T-STORMS WILL IMPACT THE GA WATERS THIS EVENING...A COUPLE
THAT MIGHT BE STRONG WITH GUSTY WINDS AND FREQUENT LIGHTNING
STRIKES.

WEDNESDAY THROUGH SUNDAY... A BRIEF SURGE OF NORTHEAST
WINDS/BUILDING SEAS ARE EXPECTED IN THE WAKE OF COLD FROPA WEDNESDAY
AM. THEN...THE GRADIENT AND ASSOCIATED WINDS SHOULD RELAX AND VEER
THROUGH THE E/SE TOWARD THE S/SW WEDNESDAY PM THROUGH THURSDAY AS
SURFACE HIGH PRESSURE SHIFTS OFFSHORE. AHEAD OF ANOTHER APPROACHING
COLD FRONT...S/SW WINDS WILL INCREASE AND SEAS WILL BUILD
FRIDAY/FRIDAY NIGHT...AND SCA WINDS/SEAS COULD DEVELOP ESPECIALLY
ACROSS AMZ350 AMD AMZ374. IN THE WAKE OF COLD FROPA...COLD ADVECTION
AND STRONG/BUILDING HIGH PRESSURE WILL PRODUCE A SURGE OF NORTHEAST
WINDS/ELEVATED SEAS DURING THE LATTER HALF OF THE WEEKEND INTO EARLY
NEXT WEEK. SMALL CRAFT ADVISORIES APPEAR LIKELY WITH THIS EVENT.

MEANWHILE...HIGHER DEWPOINTS IN THE 60S ADVECTING OVER THE WATERS
COULD SUPPORT SOME SEA FOG BEGINNING THURSDAY/THURSDAY  NIGHT AND
CONTINUING UNTIL COLD FROPA OCCURS SATURDAY. WILL CONTINUE TO ASSESS.

&&

.EQUIPMENT...
NOAA WEATHER RADIO ALL HAZARDS TRANSMITTER WWH-25 OPERATING ON A
FREQUENCY OF 162.425 MHZ WILL BE OFF THE AIR FOR MAINTENANCE
UNTIL FURTHER NOTICE DUE TO PHONE LINE PROBLEMS. TELCO HAS BEEN
NOTIFIED.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...NONE.

&&

$$
SYNOPSIS...
NEAR TERM...
SHORT TERM...DPB/SPR
LONG TERM...SPR
AVIATION...
MARINE...
EQUIPMENT...



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